The present invention relates to a device for controlling the brakes of a track-bound and particularly an automatically controlled vehicle.
On automatically controlled vehicles, provision of automatic braking is indispensible since the information transmission between the vehicle and the control center may suddenly be disturbed or interrupted. Such automatic braking is effected at the highest possible deceleration rate to keep the distance travelled by the vehicle out of control as short as possible. Automatic braking is also provided in front of signals and speed restrictions in case the stop position or the prescribed reduced speed is not observed or observed too late.
Since each automatic braking operation is detrimental to the vehicle and inconvenient to the passengers, any inadvertent automatic braking should be avoided, that is, all service braking actions in front of signals and speed restrictions should take place so early that the automatic brake will not be applied. In the speed-distance diagram (FIG. 1), this means that the service braking curve BE must not intersect the automatic brake application curve ZE.
When determining automatic brake application curves, it must be ensured that the automatically braked vehicle comes to a stop in front of the prescribed stopping point or reaches the prescribed reduced speed before the speed restriction begins. To accomplish this, it is necessary to take into account the braking distance given by the initial speed and the automatic braking deceleration rate and a braking distance governed by the so-called brake activating time. This brake activating time is the time required for a pneumatic brake to change from the unoperated condition to the fully effective condition. According to recommendations of a standards committee, this time may be up to 8.5 s in the case of freight trains. The brake activating time, during which the braking effect gradually builds up, is commonly taken into account in the form of a dead time Te, and it is assumed in a first order of approximation that no braking takes place during this dead time and that full brake power is applied abruptly at the end of the dead time.
Automatic braking is not often applied. Of the automatic brakings actually initiated, only a small part are genuine emergency brake applications. The largest part of all automatic brake applications take place after service braking when the brake system is already in the operated condition when the automatic brake is applied. If such additional braking distance occasioned by the brake activating time Te is plotted against the braking deceleration already effective at the application of the automatic brake, the curve shown in FIG. 2 is obtained. It can be seen that the additional braking distance BZ decreases with the increasing service braking deceleration rate B effective at the automatic braking initiation point.